Dissertations, Theses, and Capstone Projects

Date of Degree

6-2017

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biology

Advisor

David C. Lahti

Committee Members

Jason Munshi-South

Mitchell Baker

Dustin Rubenstein

Betsy Dumont

Subject Categories

Behavior and Ethology | Evolution | Other Ecology and Evolutionary Biology

Keywords

invasive species, Herpestes, scent marking, rapid evolution, sexual selection, home range

Abstract

Introduced species provide rare opportunities to test evolutionary hypotheses in situ by creating so-called natural experiments. Natural experiments are situations in nature that resemble laboratory studies by allowing for comparisons of a “control” group (i.e., a species’ native range) with “experimental” groups (i.e., a species’ introduced range). In particular, introduced animals allow us to investigate evolutionary dynamics in complex, long-lived organisms in ways that would otherwise be impossible in a laboratory setting. One such introduced animal is the small Indian mongoose (Urva auropunctata, formerly Herpestes auropunctatus). Native to South Asia, the small Indian mongoose’s introduction to more than 70 mostly tropical island locations worldwide represents an excellent natural experiment: the dates of introduction and numbers introduced are well documented, most locations of introduction are reproductively isolated from each other and thus provide numerous experimental replicates, and most introduced populations have been reproducing for at least 200 generations. In its introduced range, the small Indian mongoose is released from interspecific competition and predation, and as a result, it has become densely populated and highly invasive. In fact, the IUCN named it one of the 100 worst invasive species on the planet. Consequently, the vast majority of the literature on this species is devoted to understanding its ecological impacts on local biodiversity. In contrast, however, relatively little is known of its ecology and natural history in its native range where, in some regions, it is protected. Lacking entirely, for instance, are data pertaining to the operation of sexual selection and its mate choice behavior. Finally, while four studies have investigated evolutionary changes that small Indian mongooses have undergone since introduction, only one has investigated adaptive changes, and this study mistakenly included individuals of a separate species in its analysis, leaving its results and conclusions uninterpretable. In this dissertation, I present an exhaustive review of the available literature on the small Indian mongoose (Chapter 1), report on the first quantitative natural history data ever collected in its native range (Chapter 2), identify, for the first time in this species, features under sexual selection (Chapter 3), and, taking advantage of its natural experiment, demonstrate the rapid adaptive evolution of two of its sexually selected traits (Chapter 4).

In Chapter 1, I review literature on all ecologically relevant information of the small Indian mongoose including, their taxonomy; native and introduced ranges, and history of introduction; basic biology; impacts as an invasive species, including their status as a failed biological control, the local species they have impacted, the various management efforts around the globe, and their role in disease transmission; and finally, their use as an evolutionary model system.

In Chapter 2, I collect basic morphological measurements of small Indian mongooses from several populations in their native range in northern India. I also radio-collared and tracked 17 individuals for several months, and estimate that home ranges sizes in the native range are comparable to, though generally smaller than, estimates in the introduced range. I also find that small Indian mongooses prefer areas of human habitation and avoid forested and open areas.

In Chapter 3, I report on an investigation of the small Indian mongoose on the island of Hawaii. I conclude that the anal pad, their scent-marking tool, is a sexually selected trait in males, as indicated by its high male-biased sexual size dimorphism, and its condition-dependence and positive relationship with body size in males, but not females. From these results, I infer that males likely use scent as a sexual signal.

Finally, in Chapter 4, in an effort to understand how sexually selected traits change after becoming established, I collect similar morphological data to those collected in Chapter 2 and Chapter 3 from three additional areas of introduction, Jamaica, St. Croix, and Mauritius. I then compare these data together with those collected from the island of Hawaii, to data from the native range in India. I find that male, but not female, anal pads decreased in size according to time since introduction, and its relation to body size and condition weakened. In addition, I find that testis size increased after introduction. My results suggest an inversion in the relative contributions to fitness of two sexually selected traits in males, demonstrated by the rapid evolution of these features after introduction. Thus, I conclude that, relative to the native range, the increased encounter rates on islands of introduction (due to the markedly denser populations) have relaxed sexual selection on scent marking in males, but intensified sperm competition. My findings demonstrate that the fitness of sexually selected traits, like any other traits under natural selection, is determined by environment in which the traits are expressed.

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